As is known, in the last few years numerous power-actuator structures have been proposed in an endeavor to achieve characteristics such as low power dissipation, both during conduction (on-state) and during switching, high input impedance and high switching speed. In particular, the trend has been to pass from bipolar transistors (having low on-dissipation) and MOS transistors (having low dissipation during switching), to hybrid components that combine the advantages of both types of transistor. Amongst these, components have been proposed—such as IGBTs (Insulated-Gate Bipolar Transistors), MCTs (MOS-Controlled Thyristors), and ESTs (Emitter Switched Thyristors)—which, in addition to reaching different levels of compromise between power dissipation during the on-state and during switching, envisage driving via an insulated-gate electrode.
Amongst the hybrid solutions proposed, the ones that have proven particular advantageous, for example because they enable a high blocking voltage (which is the maximum reverse voltage that the device can withstand without undergoing breakdown), are those based upon thyristors, which have a reduced forward voltage drop during operation, and which are driven as MOSFETs, i.e., with a control voltage applied to an insulated gate. Belonging to said category are MCTs and ESTs, which, however, have a somewhat modest reverse-bias safe-operating area (RBSOA) and long turn-off times.
In order to solve said problems, in the patent application No. WO2004102671 filed on May 19, 2003 and incorporated by reference, a power device with high switching speed based upon a thyristor has been proposed. In particular, said power device, designated by 1 in FIG. 1 of the present specification, comprises a thyristor 2 and a MOSFET 3 connected in series between two current-conduction terminals 4, 5. The power device 1 also has a driving terminal 6, which is connected to an insulated-gate electrode of the MOSFET 3 and receives a voltage for turning on or off the device, and a further terminal 7 connected to the thyristor 2, for fast extraction of charge during the turn-off of the device. In this way, upon turn-off, no current tails occur, and turn-off is very rapid. In addition, the power device does not have any parasitic components and so has a large RBSOA.
Although advantageous for the aforesaid reason, the power device 1 has, however, the drawback of not being of a standard type, in so far as it has four terminals (two control terminals and two current-conduction terminals), unlike the majority of power actuators, which have only three terminals (one control terminal and two current-conduction terminals).